Device for feeding molten metal to a continuous casting device



I. PROPERZI 3,452,808 DEVICE FOR FEEDING MOLTEN METAL TO A CONTINUOUSCASTING DEVICE July 1, 1969 Sheet Filed Aug. 5, 1966 INVENTORATTORNEY 1. PROPERZI 3,452,308

DEVICE FOR FEEDING MOLTEN METAL TO A CONTINUOUS CASTING DEVICE July 1,1969 Z of 2 Filed Aug. 3, 1966 BY hM M/ J! a ATTORNEY United StatesPatent U.S. Cl. 164-278 5 Claims ABSTRACT OF THE DISCLOSURE Thisdisclosure is of a wheel type continuous casting mold having a moltenmetal feed means which is is adjustable both in distance from the moldand in aperture for creating turbulent molten metal conditions at themold entrance.

This application relates to a device for feeding molten metal to acontinuous casting device. Devices for the continuous casting of metalsare known, wherein molten metal is continuously cast and wherefrom saidmetal is fed out, usually in the form of a continuous section or moltenbar.

Embodiments of such devices can be seen, for example, in my co-pendingU.S. Patent application No. 243,087 now U.S. Patent No. 3,261,059, andBritish Patent No. 1,014,449.

Rods, tapes or round bars obtained with such devices are, however,exposed to the drawback of showing structural defects or evensegregation of the components of a metal alloy if a metal alloy is beingcast. It has been possible to ascertain that the aforementionedshort-comings are essentially a result of the fact that the cooling orsolidification of the liquid metal take place with said liquid metal inan at rest condition in general, so that the solidified metal exhibitsas has been viewed both in macrographic and micrographic plates, acrystalline structure which is somewhat coarse and is accompanied byseparation of components.

The defects thus discovered induce serious troubles in the ensuingprocessing steps of the obtained bar or section which usually isdirectly fed in still hot state to a rolling mill to undergo suitablemechanical operations therein, such as repeated considerable reductionsof the cross-section. By this the coarse crystalline textures are brokenwith the danger of causing fissures which do not always Weld themselvesagain under the influence of the heat and pressure imparted by therolling mill cylinders; as a result flaws are formed in the rolledmetal.

To obtain a fine-grained structure while avoiding the segregation of theconstituents of the alloy in the solidified metal obtained from acontinuous metal casting device, it has been recently suggested, as isfor example, disclosed in my now abandoned U.S. patent application No.404,815 to feed at a considerable speed the molten metal from thecrucible to the meniscus or liquid plane of the continuous castingdevice. The effect of such a speed is that of inducing an energeticwhirling motion within the liquid metal which is being rapidly cooledand solidified within the device, the result being that the formation ofcoarse crystalline textures and the segregation of constituents of analloy are prevented, if the metal is alloyed. By restricting, for thesake of simplicity, the discussion to the case in which a pure metal ismelted and a rod is being obtained, it has been ascertained that theobtained rod has an extremely fine and regular crystalline structure, asdisclosed in the U.S. patent application No. 404,815 and thus it can berolled or otherwise processed without any trouble whatsoever.

It has been possible to ascertain, however, that, even holding entirelyvalid the principle of impeding the formation of coarse crystallinetextures by inducing a vigorous whirling motion within the liquid metalbeing cooled in the continuous casting device, the means suggested forachieving said result in 'the above mentioned U.S. patent applicationNo. 404,815 are not entirely satisfactory and are possessed of certaindefects that it is highly desirable to eliminate, as will clearly appearin the following.

According to said U.S. patent application No. 404,815, the cruciblewhich contains the molten metal is affixed to the framing of the deviceabove the liquid meniscus of said device, and the molten metal reachessaid meniscus by flowing within a nozzle having the shape of an elongateconduit which is sloping with respect to a vertical line, projects fromthe crucibles bottom and extends up to the immediate vicinity of saidmeniscus. The molten metal flows with a considerable momentum from thenozzle and induces a whirling motion within the liquid metal beingcooled within the device: to obtain the desired grain size in thecrystalline structure of the metal which is being solidified within thedevice, the turbulence of the liquid metal being cooled should obviouslyhave a predetermined value, and this means that the molten metal shouldbe fed out of the outlet nozzle of the crucible at a determined speed.

According to the aforementioned U.S. patent application No. 404,815 therate of flow of the molten metal from the nozzle is determined by thehead of molten metal in the crucible, that is, by the level differentialbetween the outlet orifice of the nozzle and the level of molten metalwithin the crucible.

In order that the rate of flow of molten metal from the nozzle may bevaried, it is necessary that the socalled head be varied, and thisresult is obtained by causing the level of the molten metal within thecrucible to vary.

At this stage, it is fitting to note that, in order that the advantagesobtainable with a continuous casting device embodying the teaching ofthe aforementioned U.S. patent application No. 404,815 may be achievedalong with the improved results thereof, the necessity is often felt,during a casting operation, of causing the turbulence conditions of themetal being cooled in the device to be frequently varied, thus causingalso a variation of the rate of flow of the molten metal out of theoutlet orifice of the crucible nozzle. Very often said variations ofturbulence and speed should be obtained within the shortest possibletime interval so as to avoid the formation of large areas of coarsecrystalline texture within the solidified metal such areas may bereadily spotted, for example, by examining the metal coming out of therolling mill which is coupled to the continuous casting device.

Let it be assumed, for simplicity, that the continuous casting devicealso includes a wheel having a peripheral groove, driven to a continuousand constant rotary motion, of the kind disclosed in the U.S. patentapplications No. 243,087 and No. 404,815 and in the British Patent1,014,449.

The rate of flow of the molten metal from the crucible should have,under steady operative conditions, a well defined and constant value soas to give rise to the desired turbulence rating. It may occur that thetemperature of the molten metal in the crucible undergoes evenconsiderable variations as a consequence of corresponding variationstaking place in the oven and that the efficiency of the metal coolingsystem within the device is varied for example due to pressuredifferentials of the coolant water. To make the problem quite clear, letit be assumed that during casting the temperature of the molten metalWithin the crucible undergoes a sudden increase, or that the efiiciencyof the cooling is decreased due to a decrease of the pressure of thewater which feeds the cooling system, the latter being for example ofthe kind disclosed in the U.S. patent application No. 243,087 and in theBritish Patent No. 1,014,449, aforementioned. Under these conditions,the total solidification of the metal within the device will take alonger time interval and could be regarded as having been completed incorrespondence with a section of the peripheral groove of the castingwheel placed at a distance from the liquid meniscus within the samegroove, which is greater than the distance at which it took place beforethe assumed variation. [It is thus obvious that, for maintaining thegrain size of the crystalline structure of the solidified metal equal tothe values prior to the variation, it is necessary that the turbulenceof the liquid metal being cooled be increased and, therewith, the rateof flow of the molten metal coming from the crucible nozzle.

The reverse is true whenever the temperature of the liquid metal withinthe crucible undergoes a decrease and that the efficiency of the coolingsystem is increased: if so, the turbulence of the molten metal beingcooled can be decreased.

It has also been said that, in many cases, the device, or wheel for thecontinuous casting is coupled to a rolling mill so as to form a unit forcontinuous casting and rolling wherein the conditions of the unit couldfrequently demand variations in the speed of rotation of said wheel. If,still maintaining the efiiciency of the cooling system constant, thewheel should increase its rotational speed so as to increase thesolidified metal output, one has obviously to increase the amount ofmolten metal delivered by the crucible so as to keep at a constant levelthe liquid meniscus, that is the liquid plane within the peripheralgroove of the wheel. This increased delivery of molten metal obviouslyrequires an increase of turbulence of the metal being cooled so as toavoid the formation of coarse crystals.

The contrary is true if the wheel should be rotated at a lower angularvelocity.

It has been found, in practice, that it is very difficult rapidly toincrease or decrease, according to the teaching of the U.S. patentapplication No. 404,815, the level of the molten metal within thecrucible since considerable amounts of metal should be varied and thisvariation cannot be obtained, in any case, with the rapidity which isnecessary for the requirements of the continuous casting process. It hasalso been found that the molten metal, while passing through the longnozzle underlying the crucible, meets with a considerable attritionwhich hinders and partly annuls the etfect of the variations in thelevel of the molten metal in the crucible, and said level should bebrought considerably higher than it would be necessary according totheoretical considerations. Another shortcoming of the prior art asdisclosed by the U8. patent application No. 404,815 lies in that, if itis necessary to slow the rotation speed of the wheel in which thecooling of the metal takes place and it thus becomes necessary todiminish the flow of molten metal from the crucible, the molten metalstream flowing within the nozzle and whose cross-section becomes thinnerand thinner towards the outlet bore of the nozzle due to the speedincrease, may split into droplets in its lowermost portion, thus givingrise to gaseous occlusions. A further drawback is the difficulty ofmaking long nozzles of a refractory material, adapted to conveyliquefied metals at a high temperature, such as steel, copper and theiralloys. Another shortcoming is the fact that the molten metal by fallingalong the nozzle in contact with the refractory material walls moveswith a substantially laminar flow, so that, when it comes out of thenozzle outlet (said outlet is positioned in the neighborhood of theliquid meniscus Olf the casting Wheels) it produces in the liquid metalbeing cooled a turbulence which is diminished with respect to that whichone would experience if the falling motion along the nozzle had been anon-laminar flow.

It should be borne in mind, lastly, that the nozzle undergoes quickalterations as to its liquid fiow diameter and abrasion of the materialforming said nozzle could occur, and particles of said material could beoccluded in the solidified metal with ensuing detrimental consequences.

All the above enumerated drawbacks are overcome with the deviceaccording to the present invention, an object of which is that ofproviding a quick and easy variation of the speed at which the moltenmetal coming from a crucible comes into contact with the liquid meniscuswhich is formed in the casting device to originate rapid variations ofturbulence in the liquid metal being cooled with said apparatus.

Another object is to cause the molten metal to go from the crucible tothe liquid meniscus in a vertical casting by freely falling from saidcrucible, thus doing away with the necessity of having nozzles forconveying said molten metal. The additional advantage is thus achievedthat the liquid meniscus in the groove of the casting wheel on which themolten metal coming from the crucible falls has a minimum area whichsubstantially corresponds to a section of the groove taken with ahorizontal plane containing the axis of the wheel; the cooling of theliquid metal in the vicinity of the meniscus is thus more regular thanit would be in the case in which the casting takes place through thelong nozzle of the prior art with which a liquid meniscus having alarger area was obtained, corresponding to a section of the wheel groovestill taken with a horizontal plane but not containing the axis of thewheel. These and other objects are achieved with the device according tothe invention comprising supporting members which can be verticallymoved and parallel to themselves and supporting a crucible containingthe molten metal to feed the continuous casting device and means forcontrolling the vertical displacement of said members, the cruciblebottom being fitted with a perforation positioned on the vertical lineof the liquid plane of the molten metal being cooled within the device.

To make the structural features of the device more clearlyunderstandable, an embodiment thereof will be illustrated in thefollowing, .by way of example only and without any limitation, referencebeing made to the accompany drawings, wherein:

FIGURE 1 is a diagrammatical elevational view, partly in section, of acontinuous casting machine, and

FIGURE 2 is illustrative of an enlarged detail of the device, takenalong the line IIII of FIG. 1.

FIGURE 1 is illustrative of a continuous casting machine for metalswhich is very similar, the device for feeding in the molten metal beingexcepted, to the machines described in the above mentioned U.S.copending patent applications No. 243,087, No. 404,815 and in theBritish Patent No. 1,014,449.

Said device comprises a baseplate 1 which freely and rotatably supportsthe shaft 2 of a casting wheel 3 which is rotatable about its own axisand has a peripheral casting groove 4. To the baseplate 1 is afiixed apillar 5 which supports an arm 6 carrying two wheels, 7 and 8,respectively, which freely rotate about their axes. A flexible endlessmetal tape 9 is held taut between the casting wheel 3 and the wheels 7and 8: the tension of the tape is obtained through a devicediagrammatically shown in FIG. 1 and connoted by the numeral 10, whichis not illustrated in detail for simplifying the showing in that it isof known and conventional construction and is adapted to transferdisplacements to the wheel 7 in the sense of bringing it towards andaway of the wheels 3 and 8. The endless tape 9 is moved solidly with thecasting wheel 3 in the direction indicated by the arrow in FIG. 1 andconfines, with the peripheral groove 4 of said wheel a so-called castingarea which is extended along an arc of circle defined by the peripheryof the rotary casting wheel: more precisely, said are goes from thatpoint of the periphery of the wheel 3 in which the tape 9 is keptpressed against said wheel by an idle roller 11 to the point at whichthe tape parts off said Wheel. The casting wheel is internally cooledand is also cooled from its outside by a device 13 simply anddiagrammatically shown in FIG. 1 since the cooling system is notdisclosed in detail herein and is not shown in the drawings in detailinasmuch as it is of a kind very much the same as that disclosed in theUS. patent application No. 243,087 and British Patent No. 1,014,449.

Above the casting wheel a device is provided for feeding the moltenmetal to said wheel, said device comprising a vertical guiding member 14affixed to the machine baseplate in which a vertical groove, in theshape of a dovetail, has been formed; said groove houses and guides aslide which is movable and to whose body 15 (FIGS. 1 and 2) are solidlyafiixed bracket-like members 16 which carry a crucible 17. In the slide15 a vertical screw-threaded bore is formed (not shown in the drawings), in which a long threaded shaft 16 is engaged. At the top of saidshaft is afi'ixed a wheel 19 having a helical thread engaging aworm-Wheel 20, placed horizontally and rotated whenever a rotationaldrive is imparted to a handwheel 21 afiixed to the shaft of said screw.It is apparent that a rotation in either direction of the handwheel 21caused a corresponding rotation of the threaded shaft 18 and thus alifting or a depression in vertical direction of the slide 15 and thusalso of the crucible 17. The crucible 17 holds molten metal 22 whichcontinually pours out of a melting furnace in a manner known per se andnot shown for the sake of simplicity. In FIG. 2 the crucible has beenshown partially shielded by a vault 23 lined with a refractory materialthrough which a perforation 24 (see also FIG. 1) has been formed, aflame being passed through said hole so as to sweep the liquid plane ofthe molten metal held in said crucible, a fuel for the heating flamebeing fed in a conventional way through a blowpipe 25.

On the crucible bottom a member 26 is provided through which a bore isformed, exactly positioned on the vertical line of the section of thegroove 4 which is substantially defined by a horizontal plane passingthrough the axis of the wheel 3 and is near the roller 11. Above thebore formed through the member 26 of a rod 27 is pro vided, which isvertically movable and whose displacement can be controlled throughmanually actuable members 28 and 29. For example, the member 28 cansimply consist of a head shaped as a handle, solid with the rod 27 whichin a portion intermediate its length can be screwthreaded screwably toengage a nut afiixed to the machine baseplate. By rotating the member 28the rod 27 would be either lifted or depressed according to thedirection of rotation. The member 29 could, in turn, be the head of ascrew which is intended to lock the rod 27 by impeding the displacementsthereof.

As can be seen more particularly on FIG. 2 the lower portion of the rod27 is shaped as a conical surface so that, by displacing the rod 27, itis possible to vary the flow area of member 26 from a condition ofcomplete closure to a condition of total aperture, thus varying the rateof flow, or flow in the unit of time of molten metal from the crucible.

To the bottom of the crucible 17, around the member 26, is afiixed atubular member 30, for example a stainless steel tube, having the shapeshown in the drawings and extending downwardly towards the casting wheel3.

During the operation of the device the hole of the member 26 is at leastpartially left free by the rod 27 and the metal held in the crucible,for example steel or copper or their alloys, freely falls from said holeinto the groove 4 of the casting wheel, Under normal steady operativeconditions, the groove 4, in correspondence with the casting area, isfilled with metal which, in the right side of FIG. 1 is liquid and issolid in the left portion of said figure,

the cooling and subsequent solidification of the metal taking place dueto the effect of the cooling system which is an integral part of thecasting machine.

The liquid plane or meniscus 31 of the molten metal 32 in the castingwheel is kept at a constant level substantially contained in ahorizontal plane passing through the axis of the casting wheel, and thatmeans, as outlined above, that said meniscus has an area correspondingto the minimum area of the cross-section of thecasting groove, theresult being that the cooling of the liquid metal in the neighborhood ofthe meniscus 31 takes place under conditions of utmost uniformity. Theliquid metal coming out of the hole of member 28 freely and directlyfalls onto the liquid meniscus in the casting Wheel.

The metal solidified in the casting wheel continually emerges from saidwheel in the form, for example, of a continuous rod 33 and is removedfor the subsequent uses.

It should be noticed that, since the tubular member 30 has an openingwhich communicates with the ambient atmosphere only at its lowermostend, no air renewal takes place therewithin, so that the liquidlcolumnfalling from the crucible is practically submerged by an inert gasatmosphere. The tubular member 30 also fulfills the function of avoidingthat possible droplets or spatters of molten metal falling from thecrucible may be a hazard for people standing near the machine, saiddrops being conveyed into the groove 4. The molten metal falling fromthe crucible comes into contact with the meniscus 31 of the liquid metalbeing cooled in the casting area of the wheel 3 at a speed which isessentially a function of the distance of the crucible from saidmeniscus 31, the level of the liquid plane of the molten metal Withinthe crucible being kept constant during the continuous castingoperation.

The kinetic energy of the metal falling into the casting area of thewheel 3 originates a vigorous turbulence of the metal being cooled insaid area, coarse crystalline formation being thus prevented along withsegregations of the constituents of an alloy, if the metal being cast isin alloy form.

The speed at which the molten metal falling from the crucible comes intocontact with the liquid meniscus 31 can be varied very quickly andsimply manipulating the handwheel 21 so as to lift or depress thecrucible: it is thus possible readily to obtain a solidified metalhaving a uniform crystalline structure of the desired grain size.

It is thus apparent that if, as outlined in the opening portion of thisspecification, the temperature conditions of molten metal in thecrucible, or the efficiency of the cooling system are varied, theturbulence of the liquid metal being cooled can be easily andcorrespondingly varied.

Similar considerations apply to the case in which the production ofsolidified metal should be increased or decreased.

The fact that the adjustment of the falling speed of molten metal in thepoint in which it comes into contact with the liquid meniscus 31 isobtained through a variation of the height of the crucible is ofparticular advantage since it is possible, inter alia, to effect a veryaccurate adjustment which can be varied within a wide range: the meanswhich allow the achievement of said variations are very simple andpractical both as to their constructional and operational features.

Extremely advantageous, as outlined above, is also the feed of thecasting wheel with molten metal freely falling from the crucible,inasmuch as by so doing one avoids the use of a refractory material tubeor nozzle through which the molten metal is caused to fall, a nozzlewhich would undergo rapid alterations under the action of the moltenmetal which is at a high temperature, thus avoiding also that thesolidified metal may occlude traces of the material of which the nozzleis made of, thus jeopardizing the favorable properties of the solidifiedmetal, but it is not excluded that, for low-melting metals, a nozzle canbe adopted to convey the liquid directly to the cavity and still along avertical direction which is the one permitting the best utilization ofthe gravity pull converted into kinetic energy so as to induce aturbulence during the cooling stage.

I claim:

1. In a continuous casting machine, the combination comprising arotatable casting wheel having a circumferential edge face provided witha circumferential casting groove therein; an endless travelling beltlooped about the circumference of said wheel and having an inner surfaceengaging said edge face over a portion of are for closing acorresponding portion of said groove and defining a travelling moldcavity therewith; supply means arranged to introduce molten metal intosaid travelling mold cavity for undergoing cooling and solidificationtherewithin; a crucible having an outlet aperture located upwardlyspaced from the upstream end of said travelling mold cavity; first meansoperative for varying the rate of flow of molten metal through saidoutlet opening and second means operative for varying the spacing ofsaid outlet aperture from the level of molten metal in said travellingmold cavity, whereby to vary the kinetic energy with which molten metalissuing from said outlet aperture impinges upon and mixes with themolten metal in said mold cavity.

2. In a machine as defined in claim 1, said outlet aperture having apredetermined cross-sectional area, and said first means being operativefor varying the effective cross-section of said outlet aperture betweentwo conditions in which the eflective cross-section respectivelycorresponds to 100% and to 0% of said predetermined crosssectional area.

3. In a machine as defined in claim 1, said second means being operativefor varying the spacing of said outlet from said level of molten metalin said casting groove in a direction substantially vertical to saidlevel.

4. In a machine as defined in claim 1, said supply means furthercomprising a tubular member carried by said crucible and extending fromsaid bottom wall towards said travelling mold cavity in registry withsaid outlet aperture, so that molten metal issuing from the latterpasses through said tubular member prior to entering into said moldcavity.

5. In a machine as defined in claim 4, said tubular member beingimperforate and having an upper open end rigid with said bottom wall anda lower open end proximal t0 the upstream end of said travelling moldcavity, so that molten metal passing from said outlet aperture into saidmold cavity is surrounded by said tubular member over substantially theentire distance between the former and the latter.

References Cited UNITED STATES PATENTS 315,045 4/1885 Lyman 164-278359,348 3/ 1887 Daniels 164278 X 2,659,949 11/1953 Properzi 164--2783,300,821 l/ 1967 Nichols et a1. 164-278 I. SPENCER OVERHOLSER, PrimaryExaminer.

R. S. ANNEAR, Assistant Examiner.

U.S. Cl. X.R.

